IMS X8 – Desktop DAC and Amplifier (Review)

INTRODUCTION

Despite my love for portable gear, its my desktop set-up which still captures most of my time. I use it for watching movies while my wife catches up on her TV. I use it for gaming. And I use it for music. I have my end-game headphones already (HD800S), and I have a relatively cheap but excellent sounding near-field set-up (a pair of active JBL LSR-305’s, and a pair of passive Celestion F10s). But central to this set-up is a good DAC and amp, and its this combination many of us find really hard to get right. We talk about synergy and we talk about transparency – but for me its a combination of factors including:

Sonic signature

Power output

Input and output options

Footprint and build quality

Versatility (features)

Supported formats

I already have a set-up which I’m pretty much 100% happy with (iFi iUSB, iDSD, and iTube for the speakers). It has a small foot-print, plenty of power and easily works with my LSR305’s as a pre-amp and volume control. But the desktop set-up is one I genuinely enjoy testing other options – although I have yet been able to find anything (yet) to match my iFi set-up.

A few years ago I was lucky enough to meet a fellow Kiwi (Martin Young) who had built a portable valve based amp which I really enjoyed. We conversed, I ended up reviewing the unit, and since then I’ve had the chance to look at a new desktop based DAC/amp Martin has been developing. We both think its ready now for retail sale, and this review is the culmination of Martin’s 3 years development. The fact that Martin spent so long getting things right is testament to his development ethos.

ABOUT IMS

Martin Young resides in Auckland, New Zealand – and had been working for the last five years on a portable valve amplifier design, and three of those on a desktop design to compliment his X1 portable. I’ve known Martin since 2015, and we’ve conversed regularly by email and phone – and met at one of our local Head-Fi Meets. It was a good chance to sit down with him, discuss some of the designs, and compare notes on some of the hardware expectations for different music lovers and their set-ups.

In the time I’ve known him, Martin has been very responsive to suggestions and meticulous in trying to develop the best product possible. He is someone who appreciates good music, and good design, and is someone who very much subscribes to the ethos of sounding good and measuring well. He has stockpiled a cache of vintage Raytheon 6418 valves, and these are at the heart of his portable and desktop designs.

DISCLAIMER

The IMS X8 DAC/amp that I’m reviewing today was provided to me freely as a review sample. Martin have insisted I keep the review model for my personal use, or for follow up comparisons, and I thank him for this. The retail price at time of review is ~ USD 570.

PREAMBLE

If you haven’t read any of my reviews, I suggest starting here, as it will give you an insight into my known preferences and bias.

For the purposes of this review – I used the IMS X8 as part of my desk-top set-up, but also included use with a lap-top. I’ve used my HD800S, HD600, HD660S (review tour unit) Alessandro MS Pro and HD630VB headphones, and also a variety of IEMs / ear-buds and of course my LSR305’s and a pair of passive Celestion F10 bookshelf speakers.

In the time I have spent with the X8, I have personally noticed no real change to the overall sonic presentation (burn-in), although with some electronic gear (and especially valve amps) I do appreciate this can occur. This is a purely subjective review – my gear, my ears, and my experience. Please take it all with a grain of salt – especially if it does not match your own experience.

THE PACKAGE

The IMS X8 arrived in a 210 x 250 x 85mm plain brown shipping box, which when opens reveals a simple moulded tray which holds the X8 and a wall-wart (plug and transformer). There are no other additional accessories, and I can understand this to a certain extent. As Martin said to me – they could include a generic USB cable and some interconnects, but people will have their own preferences – for quality and also for length. Rather than include something which is more than likely to be discarded, keep the package reasonably priced and leave the choice to the buyer.
Also included is a Quick Start Guide.

THE TECHNICAL SPECIFICATIONS

Model

IMS X8 Integrated DAC and Amplifier

Approximate Price

USD 570.00

Dimensions

120 x 170 x 35mm

Weight

450g

DAC Chip-set

Savi-Audio SA9227 Master DAC, Phillips PCM5102 slave DAC

Valve Stage

2 x Raytheon 6418 NOS (1984) valves

Speaker Stage

Class D

Headphone Stage

Burr Brown OPA2134

Outputs

Speakers (passive), Line-out, Headphone x 2

Inputs

USB, Analog (RCA), Phono, Bluetooth

Speaker Output Specs:

Power

50W per channel @ 4 ohm, 50W per channel @ 8 ohm

THD

0.1% THD @ 25 Watts

SNR

102 dB

Headphone Output Specs:

Power

700 mW into 8 ohm, 100 mW into 300 ohm

THD

0.00008%

Output Impedance

0.26 ohm

Format Support

Up to 384/32 PCM and up to DSD64 / 128

BUILD

External

The X8 is one of those integrated units which just screams “look at me” – or at least it does to me, and to those I’ve shown it to. Its footprint is quite small for a desktop unit – just 120 x 170 x 35mm (and that’s with the feet included). It weighs around 450g.

The outer body is solid aluminium – its actually CNC milled from a solid 1 inch thick block (Martin did this both for overall rigidity and also shielding). After the CNC milling is completed, all dimensions and surfaces are measured to a tolerance of 0.05mm. The surface is then bead blasted and anodised to produce a beautifully smooth powder finish.

The circuit board is secured using stainless steel screws to aluminium stand-offs built into the case’s flooring. This ensures perfect balance with the grounding of the case. The feet and knobs are all custom made from aircraft grade aluminium.

At the top of the enclosure is a fully transparent and beautifully fitted gorilla glass panel which gives an unobstructed view of the internals and of course also highlights the radiance of the tubes.
The front panel of the X8 is symmetrical featuring a central larger volume knob for the rear speaker outputs flanked left and right by 2 x 6.3mm headphone outputs. Outside these (on both sides of the unit) are the independent volume controls for each headphone output.

The left hand side is unadorned, but the right hand side has a single 3 way toggle switch. When toggled to the front, the in-built DAC is engaged. When the switch is at the neutral position, both the in-built DAC and Bluetooth are disengaged (this setting is ideal for analog input via line-in or vinyl). With the switch toggled to the rear, the Bluetooth receiver is engaged.

At the rear of the unit are the inputs and outputs. From left to right are:

Line analog output – for line-out signal to powered active speakers, or to another amplifier. Note that this signal is attenuated by the main volume pot (can be used as a pre-amp).

2 pairs (L/R) powered speaker posts for output to passive speakers (up to 50W per channel into 4 ohms or 30W per channel into 8 ohms)

Underneath the body are 4 milled feet with rubber rings inserted to avoid surface scratching. Aesthetically the amp is both beautifully compact, and also a real statement piece (so far I haven’t had a negative statement from anyone who’s viewed it).

Internal

Internally the X8 uses Savi Audio’s SA9227 high performance DAC chip which can stream both DSD and PCM at up to 32 bit / 384 kHz. This is coupled with a Phillips PCM5102 slave DAC. Jitter is removed by using a local oscillator in async mode.

For the output stage, all outputs are driven initially via the Raytheon 6418 NOS valves, and then to the respective amplification outputs. The tubes are all ex military with very precise specifications and Martin takes the additional step of ensuring each pair of tubes is matched to a minimum of 98% so that each pair has the same gain. The reason the Raytheon 6418’s were chosen was because of their size, tonality, precision and immunity to EMP (they were originally used in earlier Tomahawk and Patriot missile production).

After the valve stage, each output is then routed to the appropriate amplification stage. For the passive speakers – this is Martin’s own Class D topology. For the line-out, this is simply out put via the valve stage, and for the headphone output, this is via the Burr Brown OPA2134.

The Bluetooth chip-set is class 2 and has receiver sensitivity better than -82dBm. The power supply for the BT receiver is also isolated from the rest of the amplifier by a DC/DC converter for extra low noise operation.

INPUTS / OUTPUTS

For inputs, you have the choice of USB, analogue line-in (rear RCA), phono-in (rear RCA) and Bluetooth. I was able to test Bluetooth, USB and and line-in.
For outputs there are the dual headphone outputs, a line-out (ideal for connecting another amp or passive speakers), and the analog powered output (for passive speakers). I was able to test all of these.

The only real issue with all of the inputs I have is that depending on the source voltage, it is possible to drive the X8’s Ratheon tubes into distortion. Thankfully the x5iii (and indeed most FiiO DAPs) have the ability to have a variable line-out, and dropping the signal down to 75% effectively removes any distortion. It’s not ideal – but very workable.

USB Input

Using J River up-sampling, I tested the X8 with PCM up to 384 kHz and it encountered no issues. I also tried with native DSD and DSD over DoP and try as hard as I could, I couldn’t get this working. I know my set-up is fine as both will output to the iFi iDSD. Perhaps it is this unit, or could it could be the Savi-Audio drivers. Either way – its not a big issue for me, as I know I can’t hear the difference anyway – and the DSD files I have sound fine down-sampled to PCM. I have noticed some audible noise on one of my rear USB ports, and I’ve been using the iFi iPurifier 2 to eliminate this. One of the few issues I’ve had with the X8 is that with the inputs and outputs so close together, its a really tight fit.

Bluetooth Input

I love the Bluetooth option. Pairing is pretty straightforward – toggle the switch, find the unit on the iPhone (identified as POR 1007BT), and pair. First time up it asked for a pairing code (4 x 0’s) then after that, plain sailing. Range is about 10m and its pretty solid. We’ve been entertaining at home, and its really nice to have the option to control the music with my phone. My understanding is that the Bluetooth chip is receiving the stream and handing off to Savi’s DAC. Anyway – I personally notice no drop in overall quality – and the ability to have a wireless system is really handy.

Line Input

This works really well (using my X5iii docked with the K5 – and pulling line-out to the X8). The signal appears to be very clean and I’ve had no problem with any source I’ve tried so far. Even the line-in is outputting via the Ratheon tubes – so the sound is very consistent.

Headphone Outs

Its actually a really nice feature to have the dual headphone outs, with each controllable by its own volume pot. My daughter is currently 15, and already a fledgling music buff, and sometimes in the weekends we’ll have a jam session and catch up on each other’s musical discoveries. She usually grabs the HD600, I grab the HD800S, and we can set the volume for our own preference. I’ve also found the dual headphone-outs fantastic for comparing headphones when reviewing (you can get really good volume matching and quickly switch from headphone to headphone). 100 mW into a 300 ohm load is more than enough for the HD800S – and I’m only using about 20% of the pot for my usual 70 dB ave at the ear (measured with an SPL meter). Turning to full volume, the HD800S are easily reaching 95dB which is far too loud for my listening preferences. Those who listen to extreme volumes, very quiet recordings, or have very demanding headphones (eg low sensitivity planars) may need additional amplification though.

With my more portable headphones, Allesandro MS Pro and Sennheiser HD630VB, there is enough room on the pot to safely utilise both headphones, and there is no noticeable pot imbalance even at quite low volumes.

Where I’d draw the line with the X8 is with IEMs. Its simply not really designed for them (too much gain). You could lower the master volume to accommodate a more sensitive transducer – but (IMO) its not the X8’s forte. The X8 at its heart is more for a medium to high impedance load, and for speakers.

Line-Out

I use this for both my active monitors and also if I’m outputting to another amp (eg VE’s Tube based Enterprise). The really nice thing about the line-out is that its volume controlled by the central pot, so when using the LSR-305 monitors, I can completely control the volume using the X8. Again the signal is clean and clear, and this is a very good combo with the JBL’s. The volume will comfortably handle a small room – but this will depend on the active monitors you are using.

Speaker Out

This is the killer one for me. I have a pair of Celestion F10 bookshelf speakers and despite being quite old and pretty small, they still output excellent sound – especially for a pair of desktop monitors. The iFi iDSD just can’t handle their power requirements (8 ohm, 88 db/mW SPL, 70 watt output). With the X8, output is very good, and ideal for a small room / living room. We even took this system away for my brother’s 50th this year, and it proved ideal as a Bluetooth to X8 to F10 system in a small hall. We had to crank it to close to max volume, but the X8 didn’t miss a beat, and the guests loved the fact they could connect to the system via Bluetooth and be playing their own music choices. It was a great night. For me – the power output to passive speakers is one of the highlights of the X8.

HEAT / MEASUREMENTS

The X8 will get moderately warm when its been running for a while but its not excessive, and the chassis (while warm) never gets too hot to handle. Its also a pretty quiet system (in terms of noise). The one thing I was interested to see if I could measure was the X8’s linearity. Bass is surprisingly good with the HD800S and I suspected that it might have been enhanced.
Caveat – the following measurements were taken with a cheap sound-card set-up on loop-back, using line-in and headphone-out for the X8 so that I could measure the amp section. The inputs were run at around 80% so that I wouldn’t overdrive the tubes.

First up the frequency response, and what surprised me was how linear the output was. On my equipment there is very slight bloom (only about 0.2-0.3 dB) around 50 Hz, and also a slow and gradual rise from 10-20kHz (about 1 dB). The rest of the frequency response is dead flat. The rise at the top-end may be an artefact at my end, but I suspect it is the X8, as other linear amps (E17K) actually do measure dead flat. The important thing though is that above 10 kHz you’re not going to notice the change – so the X8 is essentially a very linear amp.

So what about distortion? We know the X8 has a tube output so we would expect some even order distortion. Again on my cobbled together loop-back rig, both THD and THD+N are below 0.5% for both the 300Hz and 1 kHz signals. There is clearly some even order harmonics there – but not as many as I would expect. What does all this mean in real terms? Well for starters, I’m limited by the specs of my external sound card – and I do expect that I’d get better (lower) noise floor readings and better distortion readings with a better measurement device. But what it also shows is that distortion isn’t really an issue with the X8, even at close to full volume (it drops lower the more I drop the signal). It does confirm to me that for a tube based output, the X8 is pretty clean.

Bravo Martin.

SOUND

Preface

I’m going to preface this section with a little critique I received a while ago, and my answer to it – so that you can understand why I don’t comment on some things, and why I do comment on others. I was told my review on another amp was poor because I didn’t include sections on bass, mid-range, treble, sound-stage, imaging etc – yet referred to an amp as warm, full, or lean.
Now I can understand the reference to warm / full / lean – as they are very subjective terms, and whilst I’d like to avoid their use, they are invaluable to convey my subjective observations. Comparing my NFB-12 to the Aune X1S for example – the Audio-gd does sound richer and warmer. It’s the nature of the DAC and amp which is used.

But I choose not to comment on bass, mids, treble, and most definitely not sound-stage – simply because when we are talking about a DAC/amp – IMO they shouldn’t be discussed. A DACs job is to decode the signal in as linear fashion as possible, and the amp’s job is to amplify the signal with as low distortion as possible. If the device is doing its job properly, there is no effect on bass, mids, or treble – except if hardware boost is concerned. And IME an amp does not affect sound-stage (unless there is DSP or cross-feed in play) – that is solely the realm of the transducers and the actual recording.

So we have that out of the way how does the X8 perform sonically?

Tonality

To test tonality, I usually compare (using same source/transport) with my E17K. The FiiO E17K is one of the most linear devices I own, and is essentially ruler flat from 20Hz to 20kHz. Both devices were volume matched and had my PC as source. For headphones – I used the HD630VB – mainly because the E17K may have struggled a little with the HD800S.

In subjective comparison, the X8 is warmer, richer, and fuller sounding. The E17K in comparison is edgier, more vibrant, and brighter. In comparison, the X8 is smoother, and more natural sounding.

Transparency

While I mentioned smoothness, and neutrality as well as naturalness, the one thing the X8 does not lose is overall transparency. I think this is helped by the very clean background (which in itself aids a feeling of depth or space if its in the recording). All the micro details are present, and transient notes are very clean and clear – this is particularly noticeable with the HD800S. Micro details are not smoothed, nor is anything “stuffy or hazy”.

COMPARISONS

Always a difficult topic, and especially when you have a device which has so many features. So I thought I’d approach this just looking at my desktop use, and in direct comparison to my work-horse (the iFi iDSD). In comparing, I used the full iFi stack – iUSB, iDSD and iTube vs the X8 (with iPurifier 2).

I used the devices with my HD800S. With each test – the same files were used, volume was set and matched with test tones and a calibrated SPL meter. Listening was at my average normal level of 70-75 dB. Please remember that these comparisons are completely subjective and simply my biased view on the differences. The components for the iFi system were purchased by me (the iDSD was won separately in a competition).

Feature/Attribute

IMS X8

Ifi iDSD (original)

Price

$570 – X8
$119 – iPurifier 2

$499 – iDSD
$299 + $349 (iUSB + iTube original)

Size / Footprint

Larger than just iDSD but smaller than the iDSD stack. Ideal for small desktop.

IDSD is smaller by itself but stack is larger. Again ideal for a small desktop situation.

Input Power

Via wall-wart

Via USB + battery option (~10 hrs)
iTube powered by wall-wart

As DAC (USB)

Driver-less under Linux / iOS, and can use generic Win driver (dedicated driver should provide DSD)

Driver-less under Linux / iOS, requires dedicated driver for Windows

Input support

USB, Bluetooth, Line-In

USB, COAX, optical, Line-In

Power Output Ear/Headphones

Very good power output for up to 300 ohm headphones. A little limited for more sensitive portables such as IEMs.

Excellent power output and management via gain. Will power most full sized headphones or IEMs

Power Output Speakers

Able to handle active speakers, and can use pot on to control sound. Up to 50W per channel to drive passive speakers

Able to handle active speakers, and can use pot on either iDSD or iTube to control sound. Insufficient power to drive passive speakers

Tonality / Sound

Very similar tonality to iDSD combo. Slightly warmer / richer tonally, and appears to have a little more bass response (with the HD800S).

Very much depends on whether I’m using the F10s. I intend to keep both on the desktop simply because of the small footprints, and also the added features the X8 has which the iDSD is missing. If the iDSD ever failed, the X8 would be a logical replacement for me, and I really don’t know if I’d spend the additional to have it replaced. Both have their individual strengths.

As a pure desktop device, the iDSD still reigns for me (combination of footprint, power, flexibility with gain settings, and versatility with formats). But if I look at the add-ons to get similar performance using the LSR305s (iTube), it becomes a really interesting comparison, and if I had to make a buying choice between the two it would be a real dilemma. Both have their individual strengths.

ISSUES X8

So before we get to a final conclusion and look at the overall value – does the X8 have any issues which possibly need highlighting? Well, for me they are less insurmountable issues, but more observations.

Depending on input volumes, it is still possible to overdrive the valves into distortion. Its an easy fix (lower the input volume) – but worth mentioning.

When plugging the wall-wart – you need to plug the unit first, and then the wall-wart into the socket. Doing it the other way around will result in some sparking (Martin assures me this is harmless).

If the unit is bumped, you can hear some slight tube ringing. This generally dissipates quickly and is normal with many tube based amplifiers.

The rear input/output panel is quite crammed so its quite hard to have everything fully loaded (if you use multiple inputs or outputs).

The small volume pots have some audible noise when adjusting, but its only during adjustment. The rest of the time they are dead silent.

I’d really like a gain switch (note to Martin for future development). This would help power management (more sensitive IEMs).

VALUE

This will come down to personal use and how you value each of the features. It will also depend on how “picky” you are about some of the small issues I’ve listed above. For my own personal use, the X8 has some incredible features which I really do find very handy. First is the very small footprint, yet the very high output power. The three killer features I don’t have with the iDSD set-up include the Bluetooth, the dual headphone sockets and the ability to drive both passive and active speakers.

At $570 the X8 is not a cheap option, but if I look at the features it offers, and then try to price an alternative with similar features, its actually really hard to find all of them in this price bracket. For $570 with the features the X8 has, it represents very good value if those features are important to your own set-ups.

IMS X8 SUMMARY

When I look at the IMS X8, the first things that strike me are the footprint and the sheer beauty of this little device. Its a conversation starter for sure. After that – the versatility is a really high point – and especially when you consider the ability to driver headphones and both active and passive speakers. Add in the Bluetooth, and you start to get a device which is long on features, and representing some pretty good value.

The build quality is really quite impressive and the sound quality is very good for a device in this bracket. Its pretty clean and clear, and has a nice richness and smoothness (those 2nd order harmonics at work). Power output is pretty good, and it is a good pairing with my HD800S.

Is it perfect? No – but with its features it doesn’t have to be to still represent good value. Some things which could be improved include the DSD support, the slightly scratchy volume pots, the lack of a gain switch (to help with more sensitive loads), and the crowding in the rear ports.

All in all though – the IMS X8 would be a DAC/amp I could easily switch to if my current iDSD stack ever decided to play up, and it won’t be leaving my desktop any time soon.
My usual scoring table is listed below, and for me the IMS X8 scores a very respectable 82%.

My thanks to Martin for his patience and for the opportunity to test and review this wonderful little powerhouse desktop DAC and amplifier.